The present invention pertains to the production, by flotation, of potassium chloride with a high K.sub.2 O content from the salt accumulating during the cold decomposition of carnallite or of potash salts containing carnallite.
It is known from German Patent PS 931 702 that the carnallite from the potash salt ground to the fineness required for flotation is floated in the presence of water-soluble salts of primary saturated or unsaturated alkyl amines in Q liquors which are used as the flotation media, and it is then separated from the other constituents of the potash salt to permit it to be processed into high-grade potassium chloride by means of cold decomposition or hot dissolution.
German Patent 931 702 also describes a procedure according to which the carnallite contained in the potash salt is first decomposed by a dilute liquor containing magnesium chloride and the resulting mixture of sylvite and rock salt is then floated in the decomposition liquor. With this process decomposition and flotation can be carried out simultaneously in the flotation facility. However, according to German Patent 931 702 it is also possible first to decompose the carnallite contained in the potash salt and to subject the resulting mixture to flotation, in the course of which the potassium chloride floats to the surface and is collected. For this purpose it is recommended that the carnallite contained in the potash salt, which is to start with merely coarsely ground, be decomposed in a liquor that is capable of taking up all the magnesium chloride contained in the carnallite. In the process a potassium chloride having particle size of &lt;1.0 mm is formed from the carnallite. Because the natural sylvite contained in the potash salt is intergrown to a very large extent with rock salt and sometimes with kieserite, the coarse fractions of the decomposition salt contained in the decomposition mixture must be separated out and ground before the sylvite can be extracted by flotation.
However, during the flotation of such partially ground decomposition products on a large industrial scale, considerable quantities of residues with a K.sub.2 O content of 8 to 10 wt. % accumulate. In order to extract the amount of potassium chloride corresponding to this K.sub.2 O content, these residues are dissolved, as described for example in the publication by Mohr and Bohm in Freiberger Forschungshefte", A 267 (1963), pp. 103-112.
In this way, flotation can increase the quality, i.e. the K.sub.2 O content, of the potassium chloride to no more than 45 wt. %, and the K.sub.2 O recovery is in the order of 85%. The accumulating flotation residue still contains about 8 to 10% K.sub.2 O and it has to be dissolved in order to recover this valuable material. According to the remarks made by Mohr and Bohm the fine grain size of the potassium chloride obtained by decomposition hampers the recovery of high-grade potassium chloride concentrates despite the fact that it is practically free of any intergrowths. Even when the concentrates obtained by flotation from the decomposition salt are further purified in a secondary flotation process the products obtained contain only 50 wt. % K.sub.2 O.